The formation of the source and drain contacts in a fin-shaped field effect (FinFET) transistor must overcome several obstacles. Users require low on-resistance, which would be satisfied by a heavy doping of the contacts. But such a heavy doping shortens the channel too much such that leakage is an issue. To provide low on-resistance, it is conventional to form each source/drain (S/D) contact in a recess etched into the fin using selective epitaxial growth (SEG) so as to widen the fin through the resulting SEG deposition within the fin recess.
The SEG deposition favors certain crystalline planes such that the SEG deposition does not assume the planar shape of the fin within the recess but instead assumes a diamond-shaped profile in which the angled sides of the profile are referred to as facets. The facets extend laterally from the fin such that the SEG deposition may cause neighboring fins to fuse or merge. The SEG deposition must thus be reduced for designs having a small length-of-diffusion (LOD) to prevent fin merger between adjacent FinFETs, which limits the desired reduction in on-resistance. In addition, an unstable contact landing can worsen the resistance in the facet region of minimum LOD devices. Moreover, the fin side wall surface typically has a <110> crystal orientation for n-type FinFETs. This is not the preferable direction for drivability. The on-resistance and drivability issues for n-type FinFETs thus have not been solved.
Accordingly, there is a need in the art for improved FinFETs having reduced on-resistance.